Conventionally, a table circulation guide device has been used for a table on which an object such as a workpiece, equipment, etc., is mounted and which is circulated and moved along a circuit. In a working area of a straight guide passage in the middle of the circuit, operations such as machining and assembling work are performed on the object. The circuit is composed of straight guide passages and curved guide passages. In general, the straight guide passages are working areas, and the curved guide passages are non-working areas.
Japanese Patent Application Laid-Open No. 2013-176214 discloses a linear transportation device which moves an object back and forth using a linear motor. The linear transportation device includes a base, a pair of linear drive sections provided on the base, and a slider (movable member) driven by the linear drive sections. In the linear transportation device, there are provided a first circulating device for circulating the slider from the downstream end of one (forth movement side) linear drive section to the upstream end of the other (back movement side) linear drive section, and a second circulating device for circulating the slider from the downstream end of the other (back movement side) linear drive section to the upstream end of the one (forth movement side) linear drive section.
Japanese Patent Application Laid-Open No. 2000-346065 discloses a linear and curved line universal guide device which is adapted to the case where a track rail has two curved portions curved in directions different from each other. Even such a case, the guide device allows a slider to continuously move in these curved portions along the track rail. The linear and curved line universal guide device includes a track rail having a straight portion and an arc-shaped, curved portion having a predetermined radius of curvature; and a slider which has a generally saddle-shaped cross section, is disposed to straddle the track rail, and moves along the track rail as a result of rolling of a large number of balls which circulate endlessly. A load-carrying rolling groove in which the balls roll is linearly formed in the slider, and the width of the track rail at the curved portions is set to be smaller than the width of the straight portion.
U.S. Pat. No. 5,086,705 discloses a linear positioning system which comprises a carriage which moves along a track including a straight portion and a curved portion. The carriage includes a pair of roller bearings and is configured to travel along the track via the roller bearings. When the carriage moves along the curved portion of the track, the roller bearings turn along the curved portion, thereby allowing the carriage to travel along the track.
Japanese Patent Application Laid-Open No. H11-208859 discloses a conveying system which includes a travelling support body having a bogie structure which allows a carrier to change its traveling direction as a result of being guided by a guide rail on which a travel path including straight portions and curves is formed. The carrier can freely move along the travel path using external drive power. The carrier includes a pair of guide rollers which hold the guide rail from both sides; a support member for supporting the pair of guide rollers; and a bogie shaft through which the support member is pivotably supported by the carrier. When the carrier moves through a curved portion of the guide rail, the bogie shaft allows the pair of guide rollers to turn along the guide rail, so that the carrier can smoothly moves through the curved portion.
US Publication No. 2015/0008768 A1 discloses a stator device which moves an object using a linear motor. The stator device includes an electrically energizable magnetic field generator for forming a magnetic field. The magnetic field generator comprises a stator tooth, a coil wound around the stator tooth, and a holding module for holding the magnetic field generator. A first end portion of the stator tooth is fixed to a first holding device, and a second end portion of the stator tooth is fixed to a second holding device.
US Publication No. 2016/0031648 A1 discloses a conveying device which comprises a movable carriage on which track rollers are disposed, and a track rail disposed to guide the carriage. The track rail has at least one trace face, at least one straight portion, and at least one curved portion. The track rollers are configured in such a manner that during movement of the carriage along the straight portion, exclusively the track rollers of a first group roll on the track face assigned to the straight portion, and during movement of the carriage along the curved portion, exclusively the track rollers of a second group roll on the track face assigned to the curved portion.
Incidentally, the linear transportation device disclosed in Japanese Patent Application Laid-Open No. 2013-176214 is configured such that when an object is to be moved from the forth movement side to the back movement side, the object is removed from the slider on the forth movement side to and is placed on the slider on the back movement side, and is not configured to continuously circulate the object from a straight portion to a curved portion. Since a single linear guide rail is disposed only at an end portion of the slider in the widthwise direction, if a load is applied to the slider, the slider may greatly displace due to a moment in the rolling direction. Therefore, the slider cannot bear large load. Also, in the linear and curved line universal guide device disclosed in Japanese Patent Application Laid-Open No. 2000-346065, in order to allow the slider for linear guide to travel through curved portions of the track rail, the width of the curved portions of the track rail is rendered smaller, so that rolling elements roll in a state in which a clearance is formed between the track rail and the slider. Therefore, the clearance must be controlled accurately. Also, the systems disclosed in U.S. Pat. No. 5,086,705 and Japanese Patent Application Laid-Open No. H11-208859 have a problem in that since an object is moved in a state in which the object is guided by rollers only, large load cannot be borne, unlike the case where the object is guided by a linear guide.
Also, the above-described table circulation guide device may be configured such that, in a straight rail area within which a table travels through a working area which requires stability and accuracy, the table travels on straight track rails via sliders, and in a curved rail region for returning, the table travels on curved track rails via carriages. In this case, when the state of travel of the table changes from a state in which the table travels on the curved track rail via the carriages to a state in which the table travels on the straight track rails via the sliders, a large impact, resistance, etc. may act on the table. Also, if an unbalanced load is imposed on the table, an unfavorable state, such as generation of large resistance, impact, noise, etc., occurs in a boundary region where the table moves to the straight track rails on the inner and outer sides of the circuit from the curved track rail or the curved guide rails simultaneously. Also, the unbalanced load imposed on the table may adversely affects the drive apparatus. Also, due to a difference in height between the straight track rails and the curved track rails and an error involved in attachment to a bed, the table receives a large resistance, impact, etc. in a boundary region in which the table moves from the curved rail region to the straight rail region and a boundary region in which the table moves from the straight rail region to the curved rail region. Therefore, the table circulation guide device has room for improvement of the configuration for reducing the resistance, impact, etc. acting on the table.